If they undress in front of you that's a pretty obvious sign
Also: they tend to spend a lot of time with you, when they see you they smile and or their eyes "sparkle", they miss getting your attention if you don't pay much attention suddenly, they like going out with you, if they tell you almost everything they feel/experience/think, lot's of affection(hugs etc).
More subtle body language: if their feet are aimed at you when talking, they often try to make eye contact....
It's 5 am so I forgot most of the subtle psych stuff they try to teach at uni.
Good luck on finding out what she needs and here's a wiki-how-not-to-do-it :
http://www.reddit.com/r/AskReddit/comme … ales_gave/